Wave-attenuation structures (also referred to as breakwaters) are generally classified into three different types of structures: (1) mounds of rubble or rock placed on the seabed, (2) fixed walls anchored to the seabed, and (3) floating structures anchored to the seabed with a guide pile or ground tackle.
Rubble-mound breakwaters often require a large base to be constructed on the seabed to support the weigh of the rubble. Such bases cover large areas of seabed and typically are many times wider than the above-water portion of the breakwater. Generally, in depths greater than 15 to 20 feet and in tidal ranges greater than 10 feet, construction of a rubble-mound breakwater can be both cost prohibitive and environmentally unsound.
A fixed-wall breakwater typically includes a stationary wall structure that is anchored to the seabed, such as with piles, and oriented perpendicular to the flow of waves. A drawback of typical conventional fixed-wall breakwaters is that they depend on the structural competency of the underlying soil to resist wave loads. Further, a fixed-wall breakwater presents an unsightly visual barrier and sometimes displays foul-smelling sea growth at low tide or low water level.
Floating breakwaters generally are favored over rubble-mound breakwaters and fixed-wall breakwaters because floating breakwaters generally are less cost sensitive to water depth than rubble-mound breakwaters and are less likely to obstruct the view of surrounding waters than fixed-wall breakwaters. A floating breakwater typically includes a large float structure (e.g., a concrete or plastic float) that supports one or more downwardly extending walls or keels.
To decrease wave transmission through a floating breakwater, it is known to increase the overall width of the float structure (usually to about one-quarter of the design wave length) and to increase the overall depth of the float structure and its downwardly extending walls. Unfortunately, increasing the width of a float structure increases manufacturing and transportation costs and has the undesirable effect of shading the seabed, which inhibits the growth of plant life. Additionally, since increasing the depth increases the overall load on the breakwater from oncoming waves, the overall depth of a breakwater is usually limited by the ability of the float structure to absorb and transfer wave forces into the seabed. Further, in the case of concrete breakwaters, increasing the depth of the walls adds significant weight to the breakwater. Thus, the overall depth of the walls in such breakwaters is limited by the ability of the float structure to support the added weight with sufficient freeboard.
Typical conventional floating breakwaters suffer from additional disadvantages. For example, existing floating breakwaters rely on the structural integrity of the float structure to resist wave forces, which are transferred to an anchor system and into the seabed. In addition, such breakwaters typically employ a flat surface oriented perpendicular to the flow of oncoming waves at the leading edge of the float structure. This produces standing and reflected waves at the leading edge of the float structure, which nearly doubles the magnitude of the load of an incident wave. Unfortunately, the connection points of the float structure (e.g., the connections that secure wales to the sides of a float structure) often become points of progressive failure.
Accordingly, there exists a continuing need for new and improved wave-attenuating systems.